1. Technical Field
The present invention relates to a radiographic imaging device, and particularly relates to a radiographic imaging device that captures a radiation image expressed by radiation that has passed through an imaging target portion.
2. Related Art
In recent years, radiation detectors such as flat panel detectors (FPD) and the like have been realized. In an FPD, a radiation-sensitive layer is disposed on a thin film transistor (TFT) active matrix substrate, and the FPD is capable of converting radiation directly to digital data. A radiographic imaging device that uses this radiation detector to capture radiation images expressed by irradiated radiation has been realized. A system for converting radiation in the radiation detector used in this radiographic imaging device may be an indirect conversion system that first converts radiation to light using a scintillator and then converts the converted light to electronic charges in a semiconductor layer of photodiodes or the like, or a direct conversion system that converts radiation to electronic charges in a semiconductor layer of amorphous selenium or the like, or the like. Whatever the system, there are a variety of materials that may be used in a semiconductor layer.
In this kind of radiographic imaging device, the radiographic imaging device itself may be capable of detecting when an irradiation of radiation starts, detecting when an irradiation ends, and detecting a radiation amount and suchlike. If so, there is no need to connect the radiographic imaging device with a radiation source and with an imaging control device that collectively controls the radiographic imaging device and the radiation source or the like. This is preferable in that system structure may be simplified and control by an imaging control device may be simplified.
As a technology relating to this kind of radiographic imaging device that may detect radiation irradiation states, Japanese Patent Application Laid-Open (JP-A) No. 07-201490 discloses an X-ray diagnostics device equipped with an X-ray-to-light signals conversion unit and a light-to-electric signals conversion unit. The X-ray-to-light signals conversion unit converts X-rays to light signals. The light-to-electric signals conversion unit captures the light signals converted by the X-ray-to-light signals conversion unit with a plural number of pixels and converts the light signals to electric signals. This X-ray diagnostics device is equipped with an X-ray exposure amount control unit that controls X-ray exposure amounts in accordance with the electric signal values of a portion of the pixels of the light-to-electric signals conversion unit.
JP-A No. 2004-223157 discloses a radiation imaging device including a radiation detection section that detects a radiation image of a subject, and plural radiation amount detection sections that detect amounts of radiation from the imaging subject. This radiation imaging device includes a control section that, on the basis of a state of arrangement of the radiation imaging device, decides on a mode of use of outputs of the plural radiation amount detection sections.
JP-A No. 2007-54484 discloses a radiographic imaging device that includes a radiation conversion section, in which conversion elements are plurally arranged on a substrate, and a control unit. The conversion elements convert radiation irradiated from a radiation exposure unit directly or indirectly to electric signals. The conversion elements of the radiation conversion section are connected to signal lines, and the radiation conversion section outputs signals for generating an image. During radiation exposure by the radiation exposure unit, the control unit stops the radiation exposure by the radiation exposure unit on the basis of electric signals from one or more of the conversion elements.
However, in the technologies disclosed in the above-mentioned Patent Documents, although states of irradiation of radiation may be detected by the device itself, depending on the imaging conditions of a radiation image, radiation irradiation states may not necessarily always be detected.
For example, if a radiation image is captured in a state in which only a portion of an imaging region of the radiographic imaging device is used, because an imaging target portion is a leg area or an arm area or the like, imaging is usually performed in a state in which the imaging target portion is disposed at a central portion of the imaging region. Consequently, the levels of radiation amounts obtained by pixels for radiation detection that are provided in parts of the imaging region where the imaging target portion is not disposed differ greatly from the levels of radiation amounts obtained by pixels for radiation detection that are disposed in parts of the imaging region where the imaging target portion is disposed. Therefore, if the characteristics of the respective pixels for radiation detection are fixed in common, the radiation amounts at some of the pixels may saturate or the signal-to-noise ratio (SNR) of radiation amounts at the other pixels may be very low.
As another example, when videographic radiation images are captured, radiation amounts are smaller than when still images are captured. If the characteristics of pixels for radiation detection are fixed in common for video imaging and still imaging, radiation amounts in one may be saturated and/or radiation amounts in the other may have very low SNR values.